In many electronic systems it becomes necessary to shift the voltage levels of signals travelling between circuits or devices operating at different supply voltages. For example, a digital integrated circuit may include core logic circuitry operating in conjunction with a 3 volt voltage supply and associated input/output circuitry operating in conjunction with a 5 volt voltage supply. The logic high signals output from the core logic to the I/O circuitry will be at approximately 3 volts, and therefore shifting upward is required to insure that such signals meet the input voltage threshold and noise immunity requirements of the 5 volt I/O circuitry. In the other direction, logic high signals travelling from the I/O circuitry to the core logic circuitry will be at approximately 5 volts and therefore shifting downward is required to insure that the maximum input voltage of the core circuitry is not be exceeded. There are numerous other instances where voltage shifting, upwards or downwards, is required.
Currently available voltage shifting circuits are typically of an analog design. Such analog circuits, especially those employing ratioed inverters, consume a substantial amount of power. Given the importance of power conservation in most electronic circuits and systems, the need has arisen for improved voltage shifting circuitry and methods which minimize power consumption.